1. Field of the Invention
The present invention relates generally to prosthetics, and, more specifically to a safety suction valve that synchronously actuates a latch mechanism and valve mechanism during donning/doffing of a stump socket and during use of a prosthesis, and an alignment kit/method that allows easy and inexpensive alignment of the prosthesis.
2. Background of the Related Art
It has long been appreciated that differential air pressure or xe2x80x9csuctionxe2x80x9d may be utilized to retain or xe2x80x9csuspendxe2x80x9d a prosthetic limb on an amputee""s stump. Gravitational and other forces tend to cause separation between the prosthetic limb and the patient""s residual extremity during use. This happens, for example, during the swing phase of gait, when a prosthetic leg is additionally subjected to centrifugal forces. Patients have routinely worn a variety of belts, straps, cuffs and harnesses to retain their prosthetic limbs against separation from the residual limb. But such devices are inconvenient and tend to cause chafing against the patient""s body giving rise to sores and abrasions.
The manner in which an artificial limb is suspended and/or attached to the residual limb determines the amount of control an amputee has over the prosthesis. Suction suspension typically involves the utilization of a socket liner and a xe2x80x9chardxe2x80x9d stump socket. The liner, which is usually fabricated from silicone, fits snugly over the residual limb and is, in turn, enveloped by the socket. A region of negative pressure between the liner-sheathed stump and the interior of the socket serves to hold the prosthesis upon the limb during use. The suspension method is very advantageous for the amputee. It gives the amputee the ability to better control the prosthesis and provides for useful sensory or proprioceptive feedback. Suction suspension also makes a prosthesis feel lighter as compared to other forms of suspension.
Some form of valve means is usually employed to regulate the air pressure in the socket such that undesirable pressure differentials do not prevent or complicate the donning and doffing of the socket. The valve means also maintains the suction or negative pressure once the socket has been satisfactorily clad. During donning, the patient""s liner-sheathed stump is inserted into the socket. At some stage or stages during the insertion the socket liner will form a roughly circumferential air-tight seal through contact with the hard socket. As the patient""s stump is inserted further into the socket, air pressure builds up under the stump. The provision of valve means permits air to escape from the socket until the pressure inside the socket equalizes with the ambient pressure and, hence, allows the stump to be fully inserted inside the socket. As a result, when the stump is completely inserted in the socket, the air pressure is equal inside and outside the socket. The valve means are now closed so that no air is allowed to flow into the distal end of the stump socket. Any tendency to remove the stump from the socket would increase the space between the inner socket wall and the stump, reducing the pressure inside the socket, since external air is unable to enter. The difference between the ambient pressure and the reduced pressure within the socket creates a xe2x80x9csuctionxe2x80x9d effect that acts to maintain the socket on the stump. In this manner, the prosthesis is xe2x80x9csuspendedxe2x80x9d on the patient""s stump. During removal of the stump from the socket (or doffing) the valve means are opened or adjusted so as to equalize the ambient pressure and the pressure inside the socket, thus dissipating the xe2x80x9csuctionxe2x80x9d effect and allowing for an easy removal of the stump.
There are several suction valves available in the market today. One class of valves consists of a valve and seat combination in which the valve and seat are threadably engaged. The seat is side-mounted on to the distal end of the socket and the valve/seat assembly is usually disengaged during donning and doffing. Another type of suction valve is an automatic air expulsion one-way valve which automatically exhausts air from the socket during donning, thereby permitting insertion of the stump into the socket. The one-way valve may be manually operated, during doffing, to allow air to pass from the outside into the interior of the socket.
Though the principle of employing xe2x80x9csuctionxe2x80x9d for xe2x80x9csuspendingxe2x80x9d an artificial limb is quite clear, there are some associated practical problems. One of these is the difficulty in providing a reliable and permanently effective seal at the proximal open end of the socket This issue being important in maintaining the reduced pressure inside the socket. Moreover, in some instances it is doubtful whether the suspending suctional force can independently support the weight of the lower limb prosthesis. This is problematic from a safety stand-point, because if the suspension means fail, and there is no redundant or back-up support mechanism, the artificial limb could detach from the patient""s stump.
U.S. Pat. No. 5,376,131 to Lenze et al. sets forth a socket with an elastic diaphragm that sealingly engages a patient""s stump, and hence attempts to provide an effective seal, but the local constriction due to such a tightly fitting diaphragm can result in impairment of circulation in the amputee""s residual limb. Suspension sleeves, which are substantially elongated bands fabricated from a resilient material and envelop part of the stump and part of the outer socket, have been used to provide complementary mechanical support and may additionally function in some capacity as a sealing means. But since these sleeves constrictingly grip the residual limb over a wide region they can limit limb movement or otherwise be uncomfortable.
A different approach to tackling this problem has led to the design of a socket liner which is attachable at its distal end to a socket or artificial limb. In this manner, the liner is mechanically secured and can provide additional suspension, if needed, and/or can play the role of a backup suspension means. Typically, the socket liner is equipped with a detachable attachment component, at its distal end, which mates with a locking device and hence secures the residual limb to an artificial limb. The locking devices generally employ a spring-loaded clutch mechanism or a pin-lock mechanism to lock on to the liner attachment component. This attachment component is either a barb-shaped structure or a frictionally-retained pin. These attachment components can lock in a plurality of positions which affects the overall length of the prosthesis. Though this may be advantageous in some cases, it can make it difficult for the patient to consistently achieve the same prosthetic configuration when the residual limb and the artificial limb are articulated. It should further be noted that in this mode of limb suspension the locking means and the valve means are autonomous entities which are separately invasive and additive in weight on the distal end of the socket.
Another type of suspension device which is in widespread use today is known as a roll-on suction socket. The suction socket, which is typically fabricated from silicone, is basically a long tubular structure with one open end. The distal end of the suction socket is attachable to a prosthesis via an attachment component and a locking device employing the same principle and design described above. During donning, the suction socket is turned inside out and rolled on to the residual stump in a fashion basically the same as donning a condom, being careful to avoid trapping of any air between the skin of the limb and the suction socket. Since the suction socket creates/destroys a partial vacuum at its distal end during rolling-on/rolling-off of the socket the function of a valve means are intrinsically incorporated into the donning/doffing technique. Thus, it would appear that the suction socket is a simple and effective device to suspend a prosthesis. But, this can be misleading because the suction socket may not be sealingly gripped by the hard socket, thereby converting the suction socket for all practical purposes into a xe2x80x9ctractionxe2x80x9d socket. Thus, the prosthesis is suspended onto the residual limb by a combination of the frictional adhesive traction of the suction socket and the locking retention due to the locking device. This skin traction causes an undesirable xe2x80x9ctetheringxe2x80x9d effect by pulling on the skin, thereby creating multiple skin problems, especially since the suction socket is usually not custom-fitted and is generally a relatively long tube which contacts a large area of skin on the residual limb. The length of the tube can also interfere with the mobility of the residual limb, especially in the case of below-knee amputees.
Once a desired suspension device has been assimilated into the prosthesis, the prosthesis must be laterally aligned with respect to the residual limb. A typical conventional method for alignment of a prosthesis involves the use of a multi-axis slide mechanism which allows adjustment with two degrees of freedom. The alignment is reached by adjusting the relative horizontal positioning between two plates, one of which is attached to the distal end of the socket (or to the locking device) and the other to the top end of the artificial limb. Each plate has a centrally located slot and the slots are perpendicularly oriented to one another. Once the proper alignment has been ascertained a fastening means, such as a nut/bolt/washer combination couples the residual limb with the artificial limb. Such an alignment mechanism can be hazardous. During use of the prosthesis the interface between the socket and the artificial limb is subjected to stresses and moments that can result in relative motion between the alignment plates, thus misaligning the prosthesis. Moreover, in extreme cases, the coupling plates may become laxly connected or totally unfastened, thereby, placing the patient at risk of harm. Also, the conventional alignment device not only adds excess weight to the prosthesis, but also adds to the cost since it is a complicated, intricate device which is typically fabricated from titanium. Further the size of this alignment device undesirably adds to the overall length of the prosthesis, which can be problematic when accommodating long stump lengths.
Conventional techniques have not been able to provide an effectual solution to gainfully employing the benefits of suction suspension in prosthetic devices. Several issues, in the field of prosthetics, related to suspension of an artificial limb and alignment between the residual and artificial limbs need to be addressed. These include improving the retention of the stump in the socket without sacrificing the patient""s comfort and without comprising on expense, weight and simplicity of use of the prosthesis. Moreover, there is also a need for a safe and convenient alignment kit/method to permit reliable, slip-free alignment and articulation between the residual stump and the artificial limb.
The present invention in one embodiment provides a safety suction valve that overcomes some or all of the afore-mentioned disadvantages by incorporating a redundant support scheme for securing a residual limb to an artificial limb. The safety suction valve substantially synchronously activates a latch mechanism and a valve mechanism, thereby providing superior retention of a residual stump in a stump socket and resulting in ease of donning and doffing of a stump socket by an amputee. The consolidation of the latch and valve mechanisms is an improved feature of the present invention. The invention in one embodiment also includes an alignment kit and prescribes an alignment method which result in a reliable and secure alignment between a residual limb and an artificial limb.
In accordance with one preferred embodiment of the invention a safety suction valve is provided comprising a locking pin, a plunger and a base. The top part of the locking pin is sized and shaped so as to be attachable to the distal end of a socket liner and the bottom part of the locking pin is latchable in a first cavity of the base. The bottom part of the locking pin has a medial section that is recessed, and is preferably substantially hourglass-shaped, so as to mate with a corresponding latch mechanism. The plunger is spring-loaded and is resident in a second cavity of the base and has a medial section that is recessed, and is preferably substantially hourglass-shaped, so as to lockingly mate with the recess of the locking pin. The plunger has a released or at rest state which dually latches the locking pin to the base and seals the open end of the second cavity of the base. When the safety suction valve is in use with a lower limb prosthesis, this released state provides a redundant support system for suspending the prosthesis by mechanically latching the locking pin and by maintaining a suspending suctional force between the stump and the stump socket. Conversely, the plunger has a depressed state that concurrently unlatches the locking pin and releases the suction.
In accordance with another preferred embodiment of the invention a safety suction valve is provided comprising a locking pin, a base, and a plunger assembly. The plunger assembly includes a latching plate, a plunger and a plunger mount. The top part of the locking pin is sized and shaped so as to be attachable to the distal end of a socket liner and the bottom part of the locking pin is latchable in the base. The bottom part of the locking pin has one or more recesses to lockingly mate with a protrusion of the latching plate. The plunger is spring-loaded and in resilient communication with the latching plate. The plunger has a released or at rest state which dually latches the locking pin to the base and seals a cavity of the plunger mount. When the safety suction valve is in use with a lower limb prosthesis, this released state provides a redundant support system for suspending the prosthesis by mechanically latching the locking pin and by maintaining a suspending suctional force between the stump and the stump socket. Conversely, the plunger has a depressed state that concurrently unlatches the locking pin and releases the suction.
In one preferred embodiment, the locking pin of the safety suction valve of the present invention includes one latching recess so that it latches inside the valve in a substantially repeatable single position. This is desirable when the patient needs to repeatedly and consistently achieve substantially the same prosthetic configuration when the residual and artificial limbs are articulated. In other preferred embodiments, the locking pin can include more than one recess so that it can latch at a plurality of positions in the valve, as dictated by the particular needs of the patient.
The present invention in one preferred embodiment also provides an alignment kit which includes a plurality of alignment couplers and a base having a low-profile stem. The stem may be incorporated with the base of a safety suction valve or, alternatively, may be part of an autonomous base member. Each alignment coupler has a substantially central hole to non-rotatably mate with the stem of the base. The alignment coupler hole may be situated in a multitude of eccentric locations, thereby allowing for a plurality of alignment options between the residual and artificial limbs which in turn permits an accurate alignment.
Preferably, an embodiment of the invention utilizes a laminated socket which securely substantially envelops the alignment coupler and the base, hence ensuring optimum coupling strength between the stump socket, base and alignment coupler. The alignment coupler is securably attachable to a lower limb prosthesis. Preferably, the alignment coupler is fabricated from a low-cost, light-weight, durable material such as aluminum though other materials may be employed with efficacy. The alignment coupler preferably has a modest thickness. Advantageously, these desirable features add minimally to the overall cost, weight and length of the prosthesis.
The present invention in one preferred embodiment also prescribes a method of aligning a stump to a lower limb prosthesis. The method includes the step of attaching a test socket to the lower limb prosthesis via an adjustable coupler. The stump which is sheathed with a socket liner is placed in the test socket. The required relative offset between the stump and the lower limb prosthesis is determined utilizing the adjustable coupler. The test socket is detached from the lower limb prosthesis and the adjustable coupler. An alignment coupler is selected based on the required relative offset between the stump and the lower limb prosthesis. A laminated stump socket is then fabricated. The lamination of the stump socket securely substantially envelops the base and the alignment coupler.
The preferred alignment method described herein, advantageously, permits prealignment of the prosthesis before the lamination during a single patient examination. Conventional alignment transfer may require the lamination to be performed before the alignment, and this can undesirably result in two examinations of the patient.
For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such objects and advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.
All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment(s) disclosed.